1. Technical Field
This invention relates to digital voice communication systems and, more particularly, to an arrangement for providing a communication interface for a data telephone and data terminal equipment for operation within such system.
2. Description of the Prior Art
Communication today is shaped by changes in two fundamental areas: user need and evolving technologies. Communication has shifted from an efficiency tool to a competitive necessity. It has also shifted from a focus on data availability to a broader scope of information management.
Current users are seeking increased flexibility and control in their communication environment. The ability to tailor communication applications to specific need and to change these applications rapidly are desired. These communication goals are achievable to some degree with existing data or digital telephones which utilize protocols such as AT&T's Digital Communications Protocol (DCP) or the Integrated Services Digital Network (ISDN) protocol promulgated by the International Telephone and Telegraph Consultative Committee (CCITT). These protocols respectively specify the user-network interface in defining such things as signaling (call setup) and data transfer formats for each interface in a communication link. Even though some flexibility and control are available in existing data telephones employing these protocols, the full potential of data telephones has not yet been realized by those arrangements currently available in the art.
A considerable level of flexibility and control is provided to a communication environment through currently available integrated voice and data workstations which connect to digital networks. Each workstation generally comprises a computer configured to work in a digital environment and a digital telephone connected to the computer. The computer is typically configured by a digital interface card specifically designed for the type of digital protocol with which it operates. And both the digital network and the digital telephone connect to the computer through this interface card for providing voice communications for a user.
One disadvantage in this workstation arrangement is that the computer is not able to implement some of the local features often desired by a user of the digital telephone, these features typically being defined by softkeys at the telephone. In a workstation employing an ISDN protocol, for example, messages compatible with CCITT Recommendations Q.931 are provided between the digital telephone and the computer and also between the computer and the digital network, the computer being interposed between the telephone and the network. Since all messages between the computer and the telephone must be in the protocol defined by these CCITT Recommendations, personal customization by providing features at the telephone other than those defined in the protocol is not permitted.
Another disadvantage in this arrangement is that the application software in the computer must fully understand the CCITT Recommendations Q.931 in order to be completely compatible with all signals in this format generated by both the digital network and the digital telephone. Since a program fully incorporating this recommendation is necessarily large, it limits the amount of memory in the computer that would otherwise be available for other data processing applications, or, alternatively, it requires the use of a more powerful and expensive computer having the appropriate data processing capability.
Also available in the art is a terminal adapter that provides increased flexibility and control in communicating directly with a digital network. The terminal adapter may be a device such as an ISDN telephone with an asynchronous data module for interfacing with a computer. A data terminal interface in the terminal adapter is arranged to interface with the computer in controlling those functionalities defined by CCITT Recommendations Q.931 for originating and answering a call, including such switching features as conference, transfer, call forwarding and electronic directory service. The data terminal interface also cooperates with and provides the computer with information received from the network in accordance with CCITT Recommendations Q.931, including the providing of such information as calling party name, directory number and feature status.
Like the above described workstation arrangement, this terminal adapter arrangement has the disadvantage that the associated computer is not able to implement the local features often desired by a user of the digital telephone, since the messages between the computer and the digital telephone must be in the digital protocol defined by, for example, the CCITT Recommendations and are therefore limited to these features.
Another disadvantage in this terminal adapter arrangement is that implementation of the call switching features provided by the computer also generate appearance signals at the output display of the terminal adapter. Thus if an incoming call is to be rerouted to another telephone by the computer, for example, during receipt of this incoming call from the network, the call message is routed to the computer as desired. This same call message is also simultaneously routed through the terminal adapter to display circuitry in this arrangement, however. Such action as either a visual or audible alerter in the terminal adapter is therefore activated, albeit briefly, alerting a user to respond even though this action in this instance is not desired. Outgoing call messages by the computer also generate undesirable appearance signals at the output display of the terminal adapter in this arrangement.